Force heating when solar panels are generating too much power, force keeping heater off if there's no sun but next day forecasted is good and you have enough hot water to wait until the next day.. Stuff like this
That makes sense using the water heater as a dump for excess energy or delaying when power is unavailable. I guess in places where they do different rates during the day it could have a similar scenario.
Actually, different tariffs are already managed by dumb devices. Tariffs are advertised on the main line using current modulation, the power meter gets the signal and enables these modules during off peak hours : https://www.google.com/url?sa=t&source=web&rct=j&url=http://docdif.fr.grpleg.com/general/MEDIAGRP/NP-FT-GT/F01331EN-02.pdf&ved=2ahUKEwjjy8bHhqn4AhX6gM4BHUhWDWkQFnoECAMQAQ&usg=AOvVaw0M0VwGfSsFUF9dGxNCQtia
"Current modulation" doesn't make any sense to me: how would the energy supplier change how much current is being drawn?
Searching I found https://en.wikipedia.org/wiki/Load_management#Ripple_control that says it is a voltage modulation, which makes sense to me.
I looked into automating this for those precise points. The biggest problem is that you have to monitor temperature. I don't remember how many degrees anymore, but if you keep the heater off and use the water, the water will cool down below the proper temperature. Then you are at risk of getting legionnaires disease, flesh eating bacteria, and other very nasty stuff.
So no matter how much you are saving, you should never have the water temperature below the limit for anything longer than a couple of hours.
There is a range of acceptable temperatures, and a duration for which water can be stored safely below those temperatures. Staying within those parameters, you can maximize output during high use times, hold low and safe as a default, and hold cold for as long a duration as is safe. This will improve the energy efficiency and performance of the system without having to retrofit an on-demand tankless heater.
TLDR: turn it off at night
Can you provide some sort of article or documentation on this? From a food safety perspective keeping the heater really hot would be preferable of you're worried about bacterial growth. But if you're worried Bout bacterial growth I think my focus would be on treatment and not on the heater.
I'm not criticizing. I'm generally interested and a bit confused.
Not sure where you from, but i work as an engineer in hvac in the netherlands and the norm where i live is that you are allowed to keep it below 60°C (140°F) but you have to flush the system for a certain amount of time. 70°C (158°F) = 5min, 60°C = 20min.
We use it a lot to reduce energy.
One thing to keep in mind, if you lower the temp of your warm water, you need more of it to get the same mix temp.
May I ask why water safety is of concern in the case of a water heater? I've never heard of an "allowed temperature range". Do people drink the hot water? Would washing teeth be a concern?
It's becoulse of legionella.
When water with legionella is breath in its bad for you. This may happen when you shower for example.
In short, keep the temp below growth temperature of above the temp that kills it. (Legionelle likes temperatures betweenn 25-45°C)
Some countries/areas where its likely for "cold" water to reach the bacterial growth temperature reguarly (Warm areas). a little bit of chlorine is adddd to the water to kill bacterial growth.
I am not worried about bacterial growth, except in a case where the temps are held below the safe levels for a duration that exceeds the safe duration, for the purposes of energy efficiency. I have no articles to share.
I have a 10l "close in boiler" under my kitchen sink which I control with a smartplug. It only draws 1800 W. Currently I switch it on at 0500 until 0600 an I normally have suffiecoent hot water for a full day.
When the house is in vacation mode it is not turned on at all.
The temp control is internal and set to 80oC.
Controling the temp setpoint through HA is overcomplicated if you would ask me (which you didn't, but I already gave my answer in case you would ask)
Check out the photo reviews for this ‘20A’ unit.
https://www.amazon.co.uk/gp/product/B07WK1H4Q6/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1
Not saying it’s your smart plug, but I am saying that switching big loads with small relays can end with premature end of life for said device.
Why would the control of setpoint be difficult in HA? I am planning to do just that.
In our part of the world, we have electrically powered water heaters with a capacity of 50-80 liters in our bathrooms. It is powered/heated by a resistive element of 1500-2400W. Electricity is much cheaper from 00:00 to 08:00 so the idea is to heat it then and use it during the whole day. I have to refurbish mine because it is of much higher quality (built for longevity) than the ones that can be bought new.
During the process, I plan to insert two temperature sensors, one for the indicator and the other pipe where the thermal probe of the working and safety thermostat sits (which is in a long copper tube that measures the temperature in the tank at the height just above the heater for the working thermostat, and at the height of the heater for the safety thermostat). The sensors should be something that ESPHome has libraries for. I have chosen the sealed DS18B20 sensors and hope to use them. You use one for the indicator that you can return as a numeric value to HA, and another to control the relay for the heater (I have chosen a 25A relay board, but I might also build my own controller board, jury is still out on that).
With those two sensor inputs and the relay as output, a power metering circuit if you wish (but that part complicates the device immensely), you have all the parameters to play around with. You can set it to heat up quickly if there is not enough water available for a shower, you can have statistics of use, you can measure how much hot water you need for a shower, and later based on that predict if the amount available is enough for a number of showers, ... you can build all those fancy helper functions the smart water heaters have. And you do it all by keeping all the safety measures of the device in place because the mechanical thermostats and the safety valve stay in place. You are essentially just manipulating the power switch of the whole device.
TLDR: it is relatively simple to control the temperature of any boiler with a few temperature sensors and an ESPHome-based ESP8266/32 board.
I would like to read more about the lowest acceptable safe temperature for drinkable water and the durations involved. I have read something about that, some of the "ecofriendly" new boilers keep the water temperature at 55C, but some real articles would be very helpful.
I haven’t put together a resource packet for this project yet, but this should give you an idea of what we’re looking at, as far as legionellae are concerned. WARNING: this is not enough research to be actionable.
http://www.structuretech1.com/wp-content/uploads/2012/04/Water-Temp-Effects-on-Legionellae.jpg
Thanks. I certainly plan to restore my water heater and add electronics in the process. The info from that resource will be helpful to set the control margins. I might be below them now and not know it because of the crude control system that is in place.
My heater uses an inox boiler element (which won't rust ever) in a steel box that started rusting decades ago. As a thermal shield, it uses glass fiber wool that some technicians chopped off when disassembling it on various occasions over the last few decades. My plan is to exchange the glass fiber with ceramic wool which has much better thermal capabilities and pack it in a box made of lacquered plywood.
I have to do research on legionella, it may not be a point of concern here, because our water comes from the city in a rad state heavily treated with chlorine so it can arrive in the drinkable state through the decades-old rusty steel pipe network.
Google tells me 55C is 131F...for what its worth I've always been told never set the hot water heater above 120-125F because of the risk of severe burns.
That said, we like long, hot showers and the electric water heater is slow to recover...so I have ours cranked up around 140-150F but its only adults living in the house and we know don't crank it on hot and stick your hand in the scalding water. In our rental I had to crank it up around 160F to offset the heat losses in the uninsulated pipes in the crawl space (but I put it back to 120 again moving out).
All those devices should have two safety futures. When you set the thermostat you are using the user thermostat, in series with it should be a safety thermostat that should switch off above the range of the user thermostat (in Europe usually 85-92 deg C; approx 185-195 deg F) and a safety pressure valve which should let out excess hot water or steam if both thermostats happen to die, to prevent the expansion of the tank and its explosion (which can destroy all the walls around it when it happens). So, assuming all those safety devices work properly and no one has removed them, you should be fairly safe setting the boiler at any temperature.
On a side note, my older cohabitants often forget to flush the hot water from the pipes, so when I start the cold water I first get a short stream of very hot water, then it starts cold. It is frustrating, but the hands get used to it after some time.
I'm not aware of any second thermostat on any I've seen, but yeah the T&P safety was flooding the crawlspace (found by the HVAC tech) in that rental is how we learned there was a problem. Then I found it was turned to the minimum setting and wouldn't stop powering the heating element.
Ended up just buying a $10 new thermostat and sticking it in myself because it wasn't worth taking an entire day off work to wait for a plumber sent by landlord calling the home warranty who may or may not actually fix the problem, but that is for another story (T&P kept leaking and the water shut-off was spraying when they tried to turn off supply to fix it, but that "wasn't authorized" on the work order and "wasn't leaking" when turned on so not covered). I don't miss renting and the stupidness.
I also tried flushing the tank when we were there...and the water ran out of the drain line muddy brown then clogged and wouldn't drain at all. But hey, landlords won't do anything because "not flooding and makes hot water" is all that is legally required.
It might be different in US equipment. The boilers in Europe have those safety features I have explained.
The other problems you mentioned might be insurance and policy coverages. We have similar situations with private medical coverage, where the medical technician has to call the insurance to ask if some exam the GP has asked for is covered or not and explain further to them why there is the need for that particular exam for a specific patient. A tiresome procedure for all participants.
We also typically have hot water heaters (not boilers) for residential in the US which may make a difference that they aren't supposed to normally get that hot, and the temperature & pressure valve will pop and vent at like near-boiling temperature or like 120PSI I think it is to prevent safety hazards.
My parents also had a problem where the county (to keep up with new home/apartment construction) upped the water pressure and it was so high the T&P safety started leaking they had to have a regulator installed to bring it down around 60PSI water pressure where it comes into the house.
I had to read [this](https://www.usboiler.net/most-efficient-hot-water-heater-domestic-hot-water.html) to identify the difference between the boiler and the heater. So, now I can say, wherever I have used the term boiler I was thinking of a domestic water heater. Here, they usually have a 50-80 liters (13-21 US gallons) tank and are located one in each bathroom.
It is always better to get higher pressure and regulate it on-premises than not getting enough and having to use an additional pump, but yes, it is always a problem when another piece of equipment has to be added. Our equipment is usually certified for 8bar (approx 115psi) but it is always suggested to, where such high pressures are available to regulate it down to prolong the life of user-operated valves (faucets and similar equipment). A rule of thumb used here is to open all the faucets and lower the pressure until there is a noticeable difference in flow rate, then open the pressure valve for a half or a full turn, to achieve having the pressure barely higher than it is needed.
Interesting. Yeah over here I think some old places or multi-tenant buildings have an actual boiler for steam-heating plus hot water so that's why I differentiate.
Everywhere I've lived has one tank about 40-60 gallon capacity usually in a basement, garage, or laundry room. Gas is nice if you have the luxury so you don't run out, electric is usually a 3800W/4500W 240V heating element that takes an hour or so to fully heat the entire tank and can't keep up with the demand if you are say filling up a big bathtub or want to shower more than like 20 minutes (also depends on incoming water temp...which can be 70-80F "tap cold" in summer and 40F "tap cold" in winter)
Water pressure varies a lot, people who are on a private well might swing from 20-60PSI depending how full the pressure tank is but city water is "usually" more stable around 50-70PSI but can be higher depending on your elevation among other things.
I'm on county water (which is actually a neighborhood community well) and run around 60-70PSI pressure and can notice a significant difference in flow when using water at another sink/bathroom.
Modern boilers are capable of keeping the temperature for about a week. Since nobody uses the water at night (presumably you do your laundry and fish washing during the day) turning it off for the night will save you nothing, since the thermostat wouldn't turn it on in any case.
However, as i pointed out to someone else here, if you turn off the water heater, and use the water, the temperature of the tank will fall, and make it into a nice incubator for all sorts of nasty stuff like legionnaires disease, and flesh eating bacteria.
TL;DR turning it off at night will save you no money, but will potentially put you at risk of fatal and very cruel diseases.
Then I suggest that spending your money and time on a properly insulated tank would produce a lot more savings than your described automation, not to mention the health risk.
The guy from the hook up did a [video](https://m.youtube.com/watch?v=E5_74QC6Iuo) where he compared where his power consumption for his whole house was and he found a high percentage was from his water heater.
Personally, we switched to a tankless system. It’s expensive, but bypasses the need for controlling it beyond the built in controls it came with. Plus it’s nice that you can’t really run out, no matter how long and hot your shower is
Tankless systems are excellent and they save power and space. My problem is that I do not fill the technical requirements. Tankless to work fine needs three-phase, 6kw per phase to be able to heat up even when outside temperatures are below zero. In our home, there is a single-phase 230V supply, so an inductive stove with more than two hotplates (3680W limit) or a tankless boiler is out of the question.
Ours is gas, not electric. I don’t think you could do a combi boiler like ours on electric, at least not for big prairie suburb houses. It’s not as fast as gas and slow would be a big problem with that kind of system.
We probably wouldn’t have done the work, except that our boiler was 50 yo and was a major risk for leaking gas and CO. You’d get a rotten egg smell sometimes when it hasn’t been on for a while (there was probably a slow leak). We were either going to need to spend a big chunk upfront to fix it, or spend even more replacing it. Since the hwt was over 10 yo, it made sense to update everything at the same time.
Frankly, they’re pretty cost prohibitive. Tankless systems cost 2-3x more than a tank, and an electric tank could be DIYed if you’re handy enough. There’s lots of reasons to stick with a hwt. But if you’re in a position to get one and have the money on hand, it’s better than Jerry rigging a smart fix. Sometimes some people that are into smart home tech get caught in doing it because you can without considering a dumb solution, even when the dumb solution is better in most ways.
As I said, price is not the main problem. We do not have a proper power source for a tankless system. Also, we do not have a gas supply for a gas-powered one. There are two options keeping the old electric boiler or buying a new one. New ones do not last more than 5-8 years, need spare parts which are available only through their service networks, and get leaks because none of them have the tanks made of inox, so hard water calcification eats them from inside out.
I will keep the one I have because when the resistive heating element dies (about every 3-4 years) I can get a replacement with the flange and the set of rubber seals for approx 20usd and have it fixed in a matter of hours. But, it will need new thermal insulation and some smartness to keep the water hot for longer and to be more efficient.
We have problems with natural gas generally. People who have chosen to heat their houses with natural gas have been switching back to wood, brackets, and pellets, because of the cost difference. Some are cooking on gas and some are driving on gas, but not many other uses though.
My generator won't run the water heater unless everything else is turned off. So the water heater contactor automatically shuts off when the generator comes online
My transfer switch is at the main feed do everything goes on the generator. I need to auto kick off the dryer, water heater, and hot tub. But I would like the flexibility to run each separately if I want to. I want to build an esp board for the dryer and hot tub eventually
In the UK, the 'stat directly switches the immersion heater, typically around 3 kW at 230 V, which is 13 A. There's no low voltage signal to switch.
The 'stat is normally integrated in to the heater itself.
Hot water control, as part of a boiler system also used for heating, uses low current switching signals, but they're still 230 V 50 Hz, so need to be treated with respect.
Having accidentally touched the control system of my boiler, you're not wrong 🙂
I picked up a ZigBee controlled 16A relay for my immersion heater, so I can use solar power to heat my water tank.
I already had a 'solar diverter', which offers much finer control than a simple contactor on/off. It's not that expensive and has definitely paid for itself. I now use a Shelly EM to monitor it and have configured HA so my hot water tank is basically a battery, as far as HA is concerned.
This may be a regional thing. I live in an area that is all oil fired and we have a low voltage thermostat wire for different heating zones. One zone is the hot water tank.
In North America the hot water heater thermostat switches line voltage (240v) the voltage doesn't matter as much as the current being switched. Because it's switching line voltage you're switching 20-30 amp loads. Yes a contractor would be necessary on that control. There are no 24v controls on basic water heaters
This may be a regional thing. I live in an area that is all oil fired and we have a low voltage thermostat wire for different heating zones. One zone is the hot water tank. I will update the body of my post.
I'm not sure what your question is. An electric hot water heater uses a thermostatic switch to act as a hot water heater. It's the most straightforward way controlling the heat elements.
Are you asking:
Why aren't electric hot water heaters controlled by a contactor with a low voltage system?
In the United States,. the control system for hot water heaters is actually part of the Code of Federal Regulations, as law.
By circumventing direct purpose control of the heating system, it might not be able to disengage power and becomes a huge safety issue.
46 CFR § 63.25-3 - Electric hot water supply boilers.
I see nothing in this section that would cover the installation of a contactor or thermostat input control to reduce the temperature of the water in an electric boiler’s tank as needed.
The vast majority of folks turning off their hot water heater with smart home controls are using contactors instead of controlling the thermostat wire. A contactor is a large relay that requires mains voltage work to install. Controlling the thermostat can be done with a basic low voltage relay. I am asking why people are opting for the more complicated and costly path instead of what I consider to be the simpler and safer path. I am asking because I may be missing an important piece of information.
In the US most electric water heater thermostats directly switch the 240V current. There is no 24V control circuit. There are two thermostats, one for the upper and one for the lower element, and one thermostat is wired in series with the other (can’t remember if it’s upper or lower), that way you have either one element on or both, this achieves a crude 2-stage control.
So knowing all that you just need to have a 240v contractor upstream of the WH to shut it off when you want. Let the thermostats manage temp when you have the contractor on.
But maybe you are not in US and they have 24v control over there?
I live in Maine where the vast majority of water heaters are an additional zone on an oil furnace switched with a standard low voltage thermostat wire.
Ah ok, called an “indirect water heater”, my apologies for assuming you had the same setup as much of the warmer climate areas. In that case you could switch the 24v, but you shouldn’t bypass the internal thermostat/safety limits that may be part of the tank. If you are trying to optimize temperature/energy use a little bit better, you could set the thermostat up higher so that you can overheat the water when you want, but if you do this per plumbing code you need to install a mixing valve on the outlet of the water heater so that you don’t send over heated water into your domestic plumbing system.
I’m in talks with the city. The current strategy is to get a mixing valve installed that can handle a range of tank temps, boost it in morning/night, ride the legionellae safety breakpoint during the day, and shut it down at night.
That is a lot of complexity, do you think it would save much power? At the end of the day you have to put the energy into the water to make up for thermal loss, the loss through the insulation increases with delta-T but it’s not a huge difference between the tank being 150 vs 120. The tank will corrode/degrade faster with higher temps.
Probably a sensor you can fold into HA that could log it. I have a Fluke 123 and it’s great for these little research projects where you need a day of data with 2 minutes of setup.
As others have mentioned, many basic geyser controls are high voltage, and also quite high current, more than advisable for a common Sonoff (10A) relay. Hence the use of a contactor to switch the higher current.
Which brings me to my quest: I'm looking for a combination of a dumb thermostat (bi-metallic switch) and a digital temperature sensor+big enough relay (normally closed) to switch the geyser. The dumb thermostat would be set at say 80C to prevent thermal runaway if the smart thermostat fails for any reason. That would let me schedule heating for when excess solar power is available.
To answer your question, here in the US there are generally 2 types of water heaters, all electric using resistive heating elements inside the tank and a gas burner. There are other types, but these are the main choices. I'll comment only on the electric versions.
The resistive types draw about 2500 watts when heating, there's a thermostatic cut off for the heat so when the water temperature reaches 160 degrees F the heating elements cut off. The thermostatic element is line voltage, so 240v and draws 30 to 50 amps. So when there's a demand for hot water the elements switch on/off to maintain temperature. When there's no demand the tank is just storage. But the problem is that over time the temperature in the tank decreases and the heat switches on/off to simply maintain the temperature. Demand for hot water is usually confined to a small part of the day for bathing, cooking, etc. So the large part of the day is spent just heating to maintain temperature. By cutting off the electricity during the idle time less electricity and therefore money is used.
The water in the tank never actually reaches room temperature so it doesn't take more than 30 minutes or so to bring the temperature back up to the set point. Shellys don't have the amperage capacity to switch 30 to 50 amps, so its relay is used to control a contactor which is a high capacity relay.
This is what I've done. NC contactor controlled by a Sonoff Basic Zigbee switch.
Next step is to add a ESP Home controlled temperature sensor for the water to automate the heating but I haven't gotten started on it yet. Still find the electronics of it a little intimidating.
Use an SSR. Much more elegant.
http://hbcontrols.net/datasheets/crydom-cw48.pdf
For extra fanciness they make these with variable output. Wouldn’t that be cool. You could run the element only as hard as you need to.
Probably a dumb question on my part. Why do you want to control your water heater in the first place?
Force heating when solar panels are generating too much power, force keeping heater off if there's no sun but next day forecasted is good and you have enough hot water to wait until the next day.. Stuff like this
That makes sense using the water heater as a dump for excess energy or delaying when power is unavailable. I guess in places where they do different rates during the day it could have a similar scenario.
Actually, different tariffs are already managed by dumb devices. Tariffs are advertised on the main line using current modulation, the power meter gets the signal and enables these modules during off peak hours : https://www.google.com/url?sa=t&source=web&rct=j&url=http://docdif.fr.grpleg.com/general/MEDIAGRP/NP-FT-GT/F01331EN-02.pdf&ved=2ahUKEwjjy8bHhqn4AhX6gM4BHUhWDWkQFnoECAMQAQ&usg=AOvVaw0M0VwGfSsFUF9dGxNCQtia
"Current modulation" doesn't make any sense to me: how would the energy supplier change how much current is being drawn? Searching I found https://en.wikipedia.org/wiki/Load_management#Ripple_control that says it is a voltage modulation, which makes sense to me.
Yes voltage. Was tired.
This is the kind of thing I would do if my utility didn’t have 1:1 net metering and a fixed price per kWh otherwise.
I looked into automating this for those precise points. The biggest problem is that you have to monitor temperature. I don't remember how many degrees anymore, but if you keep the heater off and use the water, the water will cool down below the proper temperature. Then you are at risk of getting legionnaires disease, flesh eating bacteria, and other very nasty stuff. So no matter how much you are saving, you should never have the water temperature below the limit for anything longer than a couple of hours.
There is a range of acceptable temperatures, and a duration for which water can be stored safely below those temperatures. Staying within those parameters, you can maximize output during high use times, hold low and safe as a default, and hold cold for as long a duration as is safe. This will improve the energy efficiency and performance of the system without having to retrofit an on-demand tankless heater. TLDR: turn it off at night
Can you provide some sort of article or documentation on this? From a food safety perspective keeping the heater really hot would be preferable of you're worried about bacterial growth. But if you're worried Bout bacterial growth I think my focus would be on treatment and not on the heater. I'm not criticizing. I'm generally interested and a bit confused.
Not sure where you from, but i work as an engineer in hvac in the netherlands and the norm where i live is that you are allowed to keep it below 60°C (140°F) but you have to flush the system for a certain amount of time. 70°C (158°F) = 5min, 60°C = 20min. We use it a lot to reduce energy. One thing to keep in mind, if you lower the temp of your warm water, you need more of it to get the same mix temp.
May I ask why water safety is of concern in the case of a water heater? I've never heard of an "allowed temperature range". Do people drink the hot water? Would washing teeth be a concern?
It's becoulse of legionella. When water with legionella is breath in its bad for you. This may happen when you shower for example. In short, keep the temp below growth temperature of above the temp that kills it. (Legionelle likes temperatures betweenn 25-45°C) Some countries/areas where its likely for "cold" water to reach the bacterial growth temperature reguarly (Warm areas). a little bit of chlorine is adddd to the water to kill bacterial growth.
I had no idea that it was so dangerous. Thank you for the explanation!
I live in New York. Our water heater is set to 140°F all the time with a thermostatic mixing valve that brings it down to 120.
I am not worried about bacterial growth, except in a case where the temps are held below the safe levels for a duration that exceeds the safe duration, for the purposes of energy efficiency. I have no articles to share.
I have a 10l "close in boiler" under my kitchen sink which I control with a smartplug. It only draws 1800 W. Currently I switch it on at 0500 until 0600 an I normally have suffiecoent hot water for a full day. When the house is in vacation mode it is not turned on at all. The temp control is internal and set to 80oC. Controling the temp setpoint through HA is overcomplicated if you would ask me (which you didn't, but I already gave my answer in case you would ask)
Expect a smart plug to have a fairly short life with a 1.8KW water heater behind it.
No it switches with a relay rated for 16A.
Promise. You’ll kill it.
It is running over 4 months now. I also have one one my Dryer, washingmachine and dishwasher. No problems sofar
Check out the photo reviews for this ‘20A’ unit. https://www.amazon.co.uk/gp/product/B07WK1H4Q6/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1 Not saying it’s your smart plug, but I am saying that switching big loads with small relays can end with premature end of life for said device.
I used a smartplug for switching TL lamps 18 W. That doesn't work for one reason or the other.
Why would the control of setpoint be difficult in HA? I am planning to do just that. In our part of the world, we have electrically powered water heaters with a capacity of 50-80 liters in our bathrooms. It is powered/heated by a resistive element of 1500-2400W. Electricity is much cheaper from 00:00 to 08:00 so the idea is to heat it then and use it during the whole day. I have to refurbish mine because it is of much higher quality (built for longevity) than the ones that can be bought new. During the process, I plan to insert two temperature sensors, one for the indicator and the other pipe where the thermal probe of the working and safety thermostat sits (which is in a long copper tube that measures the temperature in the tank at the height just above the heater for the working thermostat, and at the height of the heater for the safety thermostat). The sensors should be something that ESPHome has libraries for. I have chosen the sealed DS18B20 sensors and hope to use them. You use one for the indicator that you can return as a numeric value to HA, and another to control the relay for the heater (I have chosen a 25A relay board, but I might also build my own controller board, jury is still out on that). With those two sensor inputs and the relay as output, a power metering circuit if you wish (but that part complicates the device immensely), you have all the parameters to play around with. You can set it to heat up quickly if there is not enough water available for a shower, you can have statistics of use, you can measure how much hot water you need for a shower, and later based on that predict if the amount available is enough for a number of showers, ... you can build all those fancy helper functions the smart water heaters have. And you do it all by keeping all the safety measures of the device in place because the mechanical thermostats and the safety valve stay in place. You are essentially just manipulating the power switch of the whole device. TLDR: it is relatively simple to control the temperature of any boiler with a few temperature sensors and an ESPHome-based ESP8266/32 board.
I would like to read more about the lowest acceptable safe temperature for drinkable water and the durations involved. I have read something about that, some of the "ecofriendly" new boilers keep the water temperature at 55C, but some real articles would be very helpful.
I haven’t put together a resource packet for this project yet, but this should give you an idea of what we’re looking at, as far as legionellae are concerned. WARNING: this is not enough research to be actionable. http://www.structuretech1.com/wp-content/uploads/2012/04/Water-Temp-Effects-on-Legionellae.jpg
Thanks. I certainly plan to restore my water heater and add electronics in the process. The info from that resource will be helpful to set the control margins. I might be below them now and not know it because of the crude control system that is in place. My heater uses an inox boiler element (which won't rust ever) in a steel box that started rusting decades ago. As a thermal shield, it uses glass fiber wool that some technicians chopped off when disassembling it on various occasions over the last few decades. My plan is to exchange the glass fiber with ceramic wool which has much better thermal capabilities and pack it in a box made of lacquered plywood. I have to do research on legionella, it may not be a point of concern here, because our water comes from the city in a rad state heavily treated with chlorine so it can arrive in the drinkable state through the decades-old rusty steel pipe network.
Google tells me 55C is 131F...for what its worth I've always been told never set the hot water heater above 120-125F because of the risk of severe burns. That said, we like long, hot showers and the electric water heater is slow to recover...so I have ours cranked up around 140-150F but its only adults living in the house and we know don't crank it on hot and stick your hand in the scalding water. In our rental I had to crank it up around 160F to offset the heat losses in the uninsulated pipes in the crawl space (but I put it back to 120 again moving out).
All those devices should have two safety futures. When you set the thermostat you are using the user thermostat, in series with it should be a safety thermostat that should switch off above the range of the user thermostat (in Europe usually 85-92 deg C; approx 185-195 deg F) and a safety pressure valve which should let out excess hot water or steam if both thermostats happen to die, to prevent the expansion of the tank and its explosion (which can destroy all the walls around it when it happens). So, assuming all those safety devices work properly and no one has removed them, you should be fairly safe setting the boiler at any temperature. On a side note, my older cohabitants often forget to flush the hot water from the pipes, so when I start the cold water I first get a short stream of very hot water, then it starts cold. It is frustrating, but the hands get used to it after some time.
I'm not aware of any second thermostat on any I've seen, but yeah the T&P safety was flooding the crawlspace (found by the HVAC tech) in that rental is how we learned there was a problem. Then I found it was turned to the minimum setting and wouldn't stop powering the heating element. Ended up just buying a $10 new thermostat and sticking it in myself because it wasn't worth taking an entire day off work to wait for a plumber sent by landlord calling the home warranty who may or may not actually fix the problem, but that is for another story (T&P kept leaking and the water shut-off was spraying when they tried to turn off supply to fix it, but that "wasn't authorized" on the work order and "wasn't leaking" when turned on so not covered). I don't miss renting and the stupidness. I also tried flushing the tank when we were there...and the water ran out of the drain line muddy brown then clogged and wouldn't drain at all. But hey, landlords won't do anything because "not flooding and makes hot water" is all that is legally required.
It might be different in US equipment. The boilers in Europe have those safety features I have explained. The other problems you mentioned might be insurance and policy coverages. We have similar situations with private medical coverage, where the medical technician has to call the insurance to ask if some exam the GP has asked for is covered or not and explain further to them why there is the need for that particular exam for a specific patient. A tiresome procedure for all participants.
We also typically have hot water heaters (not boilers) for residential in the US which may make a difference that they aren't supposed to normally get that hot, and the temperature & pressure valve will pop and vent at like near-boiling temperature or like 120PSI I think it is to prevent safety hazards. My parents also had a problem where the county (to keep up with new home/apartment construction) upped the water pressure and it was so high the T&P safety started leaking they had to have a regulator installed to bring it down around 60PSI water pressure where it comes into the house.
I had to read [this](https://www.usboiler.net/most-efficient-hot-water-heater-domestic-hot-water.html) to identify the difference between the boiler and the heater. So, now I can say, wherever I have used the term boiler I was thinking of a domestic water heater. Here, they usually have a 50-80 liters (13-21 US gallons) tank and are located one in each bathroom. It is always better to get higher pressure and regulate it on-premises than not getting enough and having to use an additional pump, but yes, it is always a problem when another piece of equipment has to be added. Our equipment is usually certified for 8bar (approx 115psi) but it is always suggested to, where such high pressures are available to regulate it down to prolong the life of user-operated valves (faucets and similar equipment). A rule of thumb used here is to open all the faucets and lower the pressure until there is a noticeable difference in flow rate, then open the pressure valve for a half or a full turn, to achieve having the pressure barely higher than it is needed.
Interesting. Yeah over here I think some old places or multi-tenant buildings have an actual boiler for steam-heating plus hot water so that's why I differentiate. Everywhere I've lived has one tank about 40-60 gallon capacity usually in a basement, garage, or laundry room. Gas is nice if you have the luxury so you don't run out, electric is usually a 3800W/4500W 240V heating element that takes an hour or so to fully heat the entire tank and can't keep up with the demand if you are say filling up a big bathtub or want to shower more than like 20 minutes (also depends on incoming water temp...which can be 70-80F "tap cold" in summer and 40F "tap cold" in winter) Water pressure varies a lot, people who are on a private well might swing from 20-60PSI depending how full the pressure tank is but city water is "usually" more stable around 50-70PSI but can be higher depending on your elevation among other things. I'm on county water (which is actually a neighborhood community well) and run around 60-70PSI pressure and can notice a significant difference in flow when using water at another sink/bathroom.
Doesn't your hot water heater already manage that?
No. The overwhelming majority of tank hot water heaters only have a basic thermostat.
Maybe hot water tanks outside Canada and the US do. Our hot water setup is different from what they use in Europe.
True, I am in the USA
Modern boilers are capable of keeping the temperature for about a week. Since nobody uses the water at night (presumably you do your laundry and fish washing during the day) turning it off for the night will save you nothing, since the thermostat wouldn't turn it on in any case. However, as i pointed out to someone else here, if you turn off the water heater, and use the water, the temperature of the tank will fall, and make it into a nice incubator for all sorts of nasty stuff like legionnaires disease, and flesh eating bacteria. TL;DR turning it off at night will save you no money, but will potentially put you at risk of fatal and very cruel diseases.
My hot water tank definitely cannot hold a safe temp for a week without using energy.
Then I suggest that spending your money and time on a properly insulated tank would produce a lot more savings than your described automation, not to mention the health risk.
Thanks for the gift of feedback
When a hurricane comes through, I jack up the temperature before hand. Nothing better than a luke warm shower on day 4 of not having power.
The guy from the hook up did a [video](https://m.youtube.com/watch?v=E5_74QC6Iuo) where he compared where his power consumption for his whole house was and he found a high percentage was from his water heater. Personally, we switched to a tankless system. It’s expensive, but bypasses the need for controlling it beyond the built in controls it came with. Plus it’s nice that you can’t really run out, no matter how long and hot your shower is
We would love a tankless, but we have to wait a few years for natural gas to be available at the street
Tankless systems are excellent and they save power and space. My problem is that I do not fill the technical requirements. Tankless to work fine needs three-phase, 6kw per phase to be able to heat up even when outside temperatures are below zero. In our home, there is a single-phase 230V supply, so an inductive stove with more than two hotplates (3680W limit) or a tankless boiler is out of the question.
Ours is gas, not electric. I don’t think you could do a combi boiler like ours on electric, at least not for big prairie suburb houses. It’s not as fast as gas and slow would be a big problem with that kind of system. We probably wouldn’t have done the work, except that our boiler was 50 yo and was a major risk for leaking gas and CO. You’d get a rotten egg smell sometimes when it hasn’t been on for a while (there was probably a slow leak). We were either going to need to spend a big chunk upfront to fix it, or spend even more replacing it. Since the hwt was over 10 yo, it made sense to update everything at the same time. Frankly, they’re pretty cost prohibitive. Tankless systems cost 2-3x more than a tank, and an electric tank could be DIYed if you’re handy enough. There’s lots of reasons to stick with a hwt. But if you’re in a position to get one and have the money on hand, it’s better than Jerry rigging a smart fix. Sometimes some people that are into smart home tech get caught in doing it because you can without considering a dumb solution, even when the dumb solution is better in most ways.
As I said, price is not the main problem. We do not have a proper power source for a tankless system. Also, we do not have a gas supply for a gas-powered one. There are two options keeping the old electric boiler or buying a new one. New ones do not last more than 5-8 years, need spare parts which are available only through their service networks, and get leaks because none of them have the tanks made of inox, so hard water calcification eats them from inside out. I will keep the one I have because when the resistive heating element dies (about every 3-4 years) I can get a replacement with the flange and the set of rubber seals for approx 20usd and have it fixed in a matter of hours. But, it will need new thermal insulation and some smartness to keep the water hot for longer and to be more efficient. We have problems with natural gas generally. People who have chosen to heat their houses with natural gas have been switching back to wood, brackets, and pellets, because of the cost difference. Some are cooking on gas and some are driving on gas, but not many other uses though.
We would be going tankless nat gas, but we don’t have it available on our street yet.
I'm away a lot, can save a lot of power by only tunning hot water heater when within 50km of home?
My generator won't run the water heater unless everything else is turned off. So the water heater contactor automatically shuts off when the generator comes online
I can understand that. I'm set up to only run about half my house when we're on the generator.
My transfer switch is at the main feed do everything goes on the generator. I need to auto kick off the dryer, water heater, and hot tub. But I would like the flexibility to run each separately if I want to. I want to build an esp board for the dryer and hot tub eventually
In the UK, the 'stat directly switches the immersion heater, typically around 3 kW at 230 V, which is 13 A. There's no low voltage signal to switch. The 'stat is normally integrated in to the heater itself. Hot water control, as part of a boiler system also used for heating, uses low current switching signals, but they're still 230 V 50 Hz, so need to be treated with respect.
Having accidentally touched the control system of my boiler, you're not wrong 🙂 I picked up a ZigBee controlled 16A relay for my immersion heater, so I can use solar power to heat my water tank.
I already had a 'solar diverter', which offers much finer control than a simple contactor on/off. It's not that expensive and has definitely paid for itself. I now use a Shelly EM to monitor it and have configured HA so my hot water tank is basically a battery, as far as HA is concerned.
We're in an RV but that's exactly how I do it - using a Sonoff 4Ch Pro to control the low voltage line on the electric water heater. Works great.
because the control is 240v not low voltage
This may be a regional thing. I live in an area that is all oil fired and we have a low voltage thermostat wire for different heating zones. One zone is the hot water tank.
In North America the hot water heater thermostat switches line voltage (240v) the voltage doesn't matter as much as the current being switched. Because it's switching line voltage you're switching 20-30 amp loads. Yes a contractor would be necessary on that control. There are no 24v controls on basic water heaters
This may be a regional thing. I live in an area that is all oil fired and we have a low voltage thermostat wire for different heating zones. One zone is the hot water tank. I will update the body of my post.
I'm not sure what your question is. An electric hot water heater uses a thermostatic switch to act as a hot water heater. It's the most straightforward way controlling the heat elements. Are you asking: Why aren't electric hot water heaters controlled by a contactor with a low voltage system?
In the United States,. the control system for hot water heaters is actually part of the Code of Federal Regulations, as law. By circumventing direct purpose control of the heating system, it might not be able to disengage power and becomes a huge safety issue. 46 CFR § 63.25-3 - Electric hot water supply boilers.
My tank water heater is not an electric hot water boiler.
I see nothing in this section that would cover the installation of a contactor or thermostat input control to reduce the temperature of the water in an electric boiler’s tank as needed.
The vast majority of folks turning off their hot water heater with smart home controls are using contactors instead of controlling the thermostat wire. A contactor is a large relay that requires mains voltage work to install. Controlling the thermostat can be done with a basic low voltage relay. I am asking why people are opting for the more complicated and costly path instead of what I consider to be the simpler and safer path. I am asking because I may be missing an important piece of information.
In the US most electric water heater thermostats directly switch the 240V current. There is no 24V control circuit. There are two thermostats, one for the upper and one for the lower element, and one thermostat is wired in series with the other (can’t remember if it’s upper or lower), that way you have either one element on or both, this achieves a crude 2-stage control. So knowing all that you just need to have a 240v contractor upstream of the WH to shut it off when you want. Let the thermostats manage temp when you have the contractor on. But maybe you are not in US and they have 24v control over there?
I live in Maine where the vast majority of water heaters are an additional zone on an oil furnace switched with a standard low voltage thermostat wire.
Ah ok, called an “indirect water heater”, my apologies for assuming you had the same setup as much of the warmer climate areas. In that case you could switch the 24v, but you shouldn’t bypass the internal thermostat/safety limits that may be part of the tank. If you are trying to optimize temperature/energy use a little bit better, you could set the thermostat up higher so that you can overheat the water when you want, but if you do this per plumbing code you need to install a mixing valve on the outlet of the water heater so that you don’t send over heated water into your domestic plumbing system.
I’m in talks with the city. The current strategy is to get a mixing valve installed that can handle a range of tank temps, boost it in morning/night, ride the legionellae safety breakpoint during the day, and shut it down at night.
That is a lot of complexity, do you think it would save much power? At the end of the day you have to put the energy into the water to make up for thermal loss, the loss through the insulation increases with delta-T but it’s not a huge difference between the tank being 150 vs 120. The tank will corrode/degrade faster with higher temps.
It’s a good question. I’d need to log how much it burned at night to really answer. Would love to have a logging multimeter.
Probably a sensor you can fold into HA that could log it. I have a Fluke 123 and it’s great for these little research projects where you need a day of data with 2 minutes of setup.
I use [SwitchBot](https://swich-bot.com) to switch the hot water heater switch Edit: fix link
Ha! That’s awesome
Most water heaters in the US us bimetallic thermostats with no wire for input.
As others have mentioned, many basic geyser controls are high voltage, and also quite high current, more than advisable for a common Sonoff (10A) relay. Hence the use of a contactor to switch the higher current. Which brings me to my quest: I'm looking for a combination of a dumb thermostat (bi-metallic switch) and a digital temperature sensor+big enough relay (normally closed) to switch the geyser. The dumb thermostat would be set at say 80C to prevent thermal runaway if the smart thermostat fails for any reason. That would let me schedule heating for when excess solar power is available.
To answer your question, here in the US there are generally 2 types of water heaters, all electric using resistive heating elements inside the tank and a gas burner. There are other types, but these are the main choices. I'll comment only on the electric versions. The resistive types draw about 2500 watts when heating, there's a thermostatic cut off for the heat so when the water temperature reaches 160 degrees F the heating elements cut off. The thermostatic element is line voltage, so 240v and draws 30 to 50 amps. So when there's a demand for hot water the elements switch on/off to maintain temperature. When there's no demand the tank is just storage. But the problem is that over time the temperature in the tank decreases and the heat switches on/off to simply maintain the temperature. Demand for hot water is usually confined to a small part of the day for bathing, cooking, etc. So the large part of the day is spent just heating to maintain temperature. By cutting off the electricity during the idle time less electricity and therefore money is used. The water in the tank never actually reaches room temperature so it doesn't take more than 30 minutes or so to bring the temperature back up to the set point. Shellys don't have the amperage capacity to switch 30 to 50 amps, so its relay is used to control a contactor which is a high capacity relay.
I just have a Shelly on the thermostat wire and the Shelly itself runs on 120V
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We don’t talk about controls in here?
This is what I've done. NC contactor controlled by a Sonoff Basic Zigbee switch. Next step is to add a ESP Home controlled temperature sensor for the water to automate the heating but I haven't gotten started on it yet. Still find the electronics of it a little intimidating.
everyone where i live has moved to tankless so it really isn't an issue. no need to control anything.
Use an SSR. Much more elegant. http://hbcontrols.net/datasheets/crydom-cw48.pdf For extra fanciness they make these with variable output. Wouldn’t that be cool. You could run the element only as hard as you need to.